Western Australia’s premier is standing by his strict COVID-19 isolation rules as hundreds of school students are plunged into 14 days of quarantine.

There is growing doubt over the sustainability of the state government’s hardline COVID-19 rules after cases were detected at Corpus Christi College, Harrisdale Senior High School and Winterfold Primary School, just days into the first term.

The entire Year 11 cohort of 212 students and their teachers at Corpus Christi must isolate for 14 days after a student tested positive.

Other students across years 7-12 are deemed casual contacts and required to get tested after the school held a whole-of-school assembly on Tuesday.

The case at Harrisdale involved the Year 12 cohort who attended an orientation program earlier this week. About 200 students who attended will be forced into 14 days quarantine.

Two teachers have also tested positive after attending a professional development day at Winterfold Primary School, which closed for deep cleaning on Wednesday.

The school reopened on Thursday with replacement teachers after isolation rules wiped out virtually all of the facility’s staff. About 27 children who were taught by an infected teacher also face 14 days quarantine, along with their close household contacts.

Remote learning will be available for students unable to attend classes.

Premier Mark McGowan has promised isolation periods will eventually be halved for COVID-infected people and their close contacts.

But despite growing backlash, the premier has insisted the rules will only change when the state reaches a yet-to-be defined higher caseload.

“We’ll eventually move to seven-day quarantining, and in certain circumstances people will still be able to go to school and go to work,” he told ABC radio.

“But at this point in time, because we have very low case numbers, we take a precautionary approach.

“If you take a less precautionary approach, you enhance the spread, more people get it and so the cycle goes on. So whilst we get vaccination rates up, caution is the order of the day.”

Mr McGowan has also refused to say when the borders will reopen after backflipping on a plan to reopen from February 5.

Qantas chair Richard Goyder and Wesfarmers chief executive Rob Scott are among the local business heavyweights who have publicly criticised the premier, saying they will relocate to the eastern states to escape his policy settings.

– AAP